PHYLOGENETICAL COMPARISON OF THE CEREBELLO-THALAMO-CORTICAL RESPONSES.

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The cerebello-thalamo-cortical responses have been intensively investigated mainly in cats and partly in monkeys and rats. Electrophysiological studies on cats were performed intracellularly as well as extracellularly in the motor cortex but no detailed intracellular studies have been reported in the parietal cortex. Recently developed intracellular HRP staining enables us to identify clearly the morphological types of recorded neurons. Moreover, there have been noted that the cerebello-cerebral responses appear to be different among cortical areas as well as animal species. In the present project, intracellular HRP staining was performed to analyze and compare the mode of the cerebellar activation of pyramidal neurons in the cat, rat and monkey cerebral cortices. In the first step of this project, we analyzed the response properties of the neurons in the cat parietal cortex. In this cortex, the mode of cerebellar activation of neurons were different from those reported in the motor cortex. Morphologically, we also revealed that the layer V pyramidal neurons in this area consist of two morphological types as previously reported in the motor and somatosensory cortices. In rats, the cerebello-cerebral responses have been reported to be different from those reported in cats and rather similar to those in the monkey motor cortex. We have already collected enough data on the responsiveness and morphologies of the deep cortical pyramidal neurons but still need to analyze the responsiveness of the superficial cortical neurons. In addition to above mentioned experiments, we performed histological studies on the cerebello-thalamic projection in monkeys with HRP and PHA-L anterograde tracing methods. These findings were partly reported in the papers.